Wrong Mini-USB-Jack

Andy Green andy at openmoko.com wrote on Mon Apr 14 13:50:27 CEST 2008
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Somebody in the thread at some point said:
| Hi,
|| In IRC we were wondering why the Freerunner, being a USB-OTG-Host
| (according to the OTG spec), only has a USB Mini-B interface (black
| jack). This means that only USB-Mini-B cables can be used in that
| jack, what causes that USB-OTG cables can't be used. The Freerunner
| is clearly a device that should have a Mini-AB port (grey jack),
| means it can be used as a client (over standard Mini-B plugs) or as a
| OTG-Host (over standard Mini-A plugs). It is only as small issue -
| the electric layout of both jacks is basically the same (means the
| Mini-B-jack can be replaced without changing layout or something else
You're right.
The apeture on the case is correct only for mini USB, so it isn't quite
painless. The OTG socket has a different profile.
Micro AB:
http://www.farnell.com/datasheets/99722.pdf
Mini B:
http://www.farnell.com/datasheets/83318.pdf
The plastic case apeture conforms closely to the Mini B profile shape.
The thing does work OK as USB host, as you say the cables are going to
be an issue.
- -Andy
------------------------------------------
This is a problem with the Nokia Internet Tablets as well. The main
feature of the USB-OTG spec is that it *automatically* puts the device
in host mode when the cable is inserted. (OTG compliant devices also
allow swapping host & peripheral modes at any time during the
connection, but I haven't yet seen any examples where that's
particularly useful. There's also a USB power control aspect, but
again the usefulness in actual practice is limited.) As the Mini A to
standard A female adapters/cables are difficult to find (Mini B to
standard A female are much more common), I just spliced together a
couple of cables I had lying around to make my own adapter cable. It
works like a charm. I have to change to host or OTG mode manually, but
that's no big deal. USB-OTG devices should work fine as a standard USB
peripheral.
It's possible, although a bit more tricky, to make your own OTG cable
with whatever plugs you need. If the device that's acting has host
doesn't supply enough current for the peripheral, you can use a
powered hub between them, although that results in regular USB
connections (you lose OTG when going through a hub).
In short, USB-OTG is more of an issue with relatively "dumb" devices
than it is with devices that are basically full-blown computers in
their own right (like the Neo and Internet Tablets).
More info:
http://www.usb.org/developers/onthego/http://www.maxim-ic.com/appnotes.cfm?appnote_number=1822&CMP=WP-3
Mark